Gliederung

Objective

The extent of brain tumour resection in the vicinity of the central region is limited by the risk of postoperative neurological deficits. Therefore, intraoperative neurophysiological techniques are indispensable during surgery in and around the motor area. The repetitive application of high-frequency anodal monopolar cortical stimulation (MCS) allows a qualitative and quantitative evaluation of compound muscle action potentials (CMAPs). The aim of this study was to investigate stimulation and recording parameters, as well as to answer the question whether there is a connection between intraoperative potential alterations, surgical manipulation and postoperative clinical condition.

Methods

In this prospective study 200 patients were submitted to monitoring during surgery in the central region. All procedures were performed under general anesthesia without muscle relaxants. The motor pathways were monitored during the entire surgical procedure by repetitive high-frequency anodal monopolar stimulation (frequency: 400-500 Hz; train: 7-10; impulse duration: 0.2-0.7 ms; stimulation intensity: 15.3 Â± 8.2 mA). CMAPs were recorded from the thenar and forearm flexor muscles and were continuously evaluated as to their latency, potential duration and amplitude. The recorded alterations were subsequently correlated with surgical maneuvers and with postoperative neurological deterioration.

Results

MCS-Mapping of the motor cortex was sucessfull in 91.8% of the cases. The monitoring parameters (latency, potential duration and amplitude) had a broad interindividual range of variation. No statistical correlation was found between potential parameters and stimulation intensity. Individual latency fluctuations of up to 5% were observed without a pathological correlate. A correlation between individual intraoperative potential changes and surgical maneuvers or postoperative neurological deterioration was observed in 20 cases (10%) . A spontaneous shift in latency of more than 15%, or a sudden reduction in amplitude of more than 80% were considered warning criteria. In all cases with irreversible changes in latency or with a complete loss of potentials there was a postoperative neurological deterioration.

Conclusions

MCS is subject to technical, anatomical and neurophysiological restrictions. Nevertheless, repetitive MCS is a reliable method for monitoring subcortical motor pathways. Changes in MEP-latency and MEP-amplitude not only serve as intraoperative warning signals but are also of prognostic value.